This invention relates to a method of manufacturing a liquid crystal display device in which the orientation of the liquid crystal molecules is controlled so as to provide a high quality display.
A field effect type liquid crystal display device is now widely used as the display element of table type electronic computers and digital wrist watches because of its low power consumption. The field effect type liquid crystal display device is constructed and operates as follows. More particularly, a liquid crystal having a positive dielectric anistropy (a liquid crystal wherein the dielectric constant along the longitudinal axis of the liquid crystal molecule is larger than that along an axis perpendicular to the longitudinal axis) is interposed between parallel upper and lower substrates made of glass, and the molecules of the liquid crystal are arranged in parallel with the interfaces between the upper and lower substrates and the liquid crystal. The orientation of the molecules is gradually twisted about 90.degree. between both interfaces. The display element is arranged between a pair of polarizing plates having axes of polarization intersecting at right angles. Then, the light incident to the display device from outside is linearly polarized by one polarizing plate, then rotated through about 90.degree. by the twisted arrangement of the molecules of the liquid crystal and then transmitted through the other polarizing plate. When a voltage of from several to several tens of volts is impressed across transparent electrodes which are mounted on the inner surfaces of the upper and lower substrates in a suitable pattern of a letter or digit, the molecules of the liquid crystal at a region in register with the electrodes applied with the voltage will come to orient in the direction of electric field which is substantially perpendicular to the direction of initial orientation of the molecules which was parallel with the interfaces. Under these conditions, the incident light will not be rotated by the molecules of the liquid crystal but will be intercepted by the other polarizing plate. Alternatively, if the display element is interposed between the upper and lower polarizing plates whose axes of polarization are parallel with each other, the incident light is intercepted by the molecules at a region in register with electrodes not applied with the voltage whereas the light is transmitted at a region in register with electrodes applied with the voltage. Thus, by the transmission and interception of the light effected by the above described operations, a digit or a pattern is displayed.
With the prior art liquid crystal display device constructed as above described, a display defect called an induced domain occurs when a voltage is impressed across the electrodes. More particularly, as will be discussed later with reference to the accompanying drawing, although the molecules of the liquid crystal tend to orient in a direction substantially parallel with the direction of the electric field when they are subjected to the field, actually they do not orient in a direction at right angles with respect to their direction of orientation under no field which is parallel with the interfaces. The orientation of the molecules of the liquid crystal occurs in such a manner that the left ends incline upwardly and the right ends incline upwardly with the same probability so that the directions of inclination of the molecules with respect to the upper substrate are different in one region from adjacent regions. For this reason, the displays in these two regions have different contrasts for the same direction of view thus causing a display including spots and degrading the quality of display markedly.
It has been proposed to provide a liquid crystal orientation layer having a directional property, that is a layer whose surface adjacent the liquid crystal has a property to orient the molecules of the liquid crystal in a definite direction when voltage is not impressed across the electrodes on the inner surfaces of the upper and lower substrates, for the purpose of eliminating the induced domain. The liquid crystal orientation layers are formed by vapor depositing a desired material on the inner surface of the upper or lower substrate from a source of vaporization disposed at a predetermined angle with respect to the inner surface of the upper or lower substrate. With prior art however, it is necessary to vary the angle of vapor deposition when the composition of the liquid crystal varies. Accordingly, the mechanism for varying the angle of vapor deposition is complicated and it has been desired to provide an improved and simple method of forming the liquid crystal orientation layers commensurate with the composition of the liquid crystal, which is suitable for the mass production of the liquid crystal display elements.